arXiv subjects

Johannes Roth

Publications and source records attributed to Johannes Roth.

22 records · Page 2Linked to original sources

arXiv2004

Quasicrystalline Order in Binary Dipolar Systems

Motivated by recent experimental findings, we investigate the possible occurrence and characteristics of quasicrystalline order in two-dimensional mixtures of point dipoles with two sorts of dipole moments. Despite the fact that the dipolar interaction potential does not exhibit an intrinsic length scale and cannot be tuned a priori to support the formation of quasicrystalline order, we find that configurations with long--range quasicrystallinity yield minima in the potential energy surface of the many particle system. These configurations emanate from an ideal or perturbed ideal decoration of a binary tiling by steepest descent relaxation. Ground state energy calculations of alternative ordered states and parallel tempering Monte-Carlo simulations reveal that the quasicrystalline configurations do not correspond to a thermodynamically stable state. On the other hand, steepest descent relaxations and conventional Monte-Carlo simulations suggest that they are rather robust against fluctuations. Local quasicrystalline order in the disordered equilibrium states can be strong.

cond-mat.other↗

arXiv1997

Icosahedral coincidence rotations

The coincidence problem for three-dimensional discrete structures with icosahedral symmetry is reinvestigated. We present a parametric description of the coincidence rotations based on special quaternions, called icosian numbers. In particular, we give a characterization of the possible coincidence indices (Sigma-factors) and present a complete list of the possible rotations with Sigma < 100.

cond-mat↗

arXiv1996

Atomic Self-Diffusion in Quasicrystals: A Molecular Dynamics Study

We present a molecular dynamics study on atomic self-diffusion in Frank-Kasper type dodecagonal quasicrystals. It is found that the quasicrystal-specific flip mechanism for atomic diffusion as predicted by Kalugin and Katz, indeed occurs in this system. However, in order to be effective, this mechanism needs to be catalyzed by other defects such as half-vacancies if the structure is truly three-dimensional. For this reason, flip diffusion is difficult to distinguish from standard vacancy diffusion. In a quasi-two-dimensional setup, however, the flips may occur without other defects. Activation energies and flip frequencies are also determined.

cond-mat↗

arXiv1996

A new binary decagonal Frank-Kasper quasicrystal phase

A structure model of atoms of two sizes, interacting with Lennard-Jones potentials and simulated by molecular dynamics, was observed to freeze into a decagonal quasicrystal dominated by Frank-Kasper coordination shells and closely related to the Henley-Elser model for icosahedral quasicrystals. Idealized structure models can be described as decorations of triangle-rectangle and rhombus tilings. Equilibrium properties of the idealized model have been determined by molecular dynamics simulations and a high stability of the model and a low jump rate of the atoms have also been observed.

cond-mat↗